1. Field of the Invention
The present invention relates to a router system, and more particularly, to a router and method for controlling a maximum transmission unit of an external network interface.
2. Description of the Related Art
FIG. 1 is a block diagram illustrating a high-capacity router 10 according to prior art, where the router 10 includes a routing processor 11, an ethernet switch 12, a switch fabric 13, and a plurality of linecard processors 15 through 18.
The routing processor 11 performs a routing function that generates and calculates a routing table and a total management function to smoothly operate the router 10. The ethernet switch 12 performs switching operations for internal data communication of the linecard processors 15 through 18, respectively. The switch fabric 13 performs high-speed switching to enable packet data transmission through data ports. The plurality of linecard processors 15 through 18 connected to the ethernet switch 12, looks up a forwarding table to determine the appropriate output port for transmitting a received data packet to other network.
The plurality of linecard processors 15 through 18 respectively include an external network interface and a network processor (not shown) which manages the look-up of the forwarding table and the packet data transmission. Each external network interface is a packet over SONET interface (POS IF) 5, an asynchronous transfer mode interface (ATM IF) 6, a gigabit ethernet interface (GE IF) 7, or a 10/100 Mbps ethernet interface (10/100M IF) 8 (hereinafter, generally referred to as external network interfaces 5 through 8).
The routing processor 11 executes programs, which update information of the routing table and forwarding table in response to a phase shift of the network. Here, the programs can include support for border gateway protocol (BGP), open shortest path first (OSPF), or Telnet, interacting with programs running in other routers. The programs are executed by the external network interfaces 5 through 8 respectively included in the linecard processors 15 through 18.
However, since the location of the executed programs and the external network interfaces 5 through 8 used in program are not identical, an operating system of the routing processor 11 provides environment that the programs can be executed smoothly via virtual network interface. Here, the virtual network interface is shaped logically, wherein the external network interfaces 5 through 8 of the linecard processor 15 through 18 are implemented in the operating system of the routing processor 11. The virtual network interfaces connected with the physical interfaces have been disclosed in U.S. Pat. No. 5,970,066, titled “Virtual ethernet interface” issued to Lowry et al. on 19, Oct. 1999 and in U.S. Pat. No. 6,330,599, titled “Virtual Interfaces with dynamic binding” issued to Harvey on 11, Dec. 2001.
In general, a network interface such as an ethernet interface has a maximum transmission unit (hereinafter, referred to as an MTU) denoting the largest number of bytes that can be transmitted at a time. Most high-capacity routers use IEEE 802.3 ethernet interface for data transmission through a virtual network interface, where the MTU of the IEEE 802.3 ethernet interface is 1,500 bytes. Thus, if an external network interface requires an MTU greater than 1,500 bytes, the virtual network interface cannot support such an MTU according to prior art.